Vehicle testing apparatus

ABSTRACT

The disclosure describes a chassis dynamometer having at least one pair of rollers for contact with at least one traction wheel of a motor vehicle, one of the rollers being braked by an eddycurrent brake the stator of which is mounted for pivotal movement in accordance with the braking torque developed against a resilient bias. A perforated disc is mounted on and for movement with the stator of the eddy-current brake, the rim of the disc being in driving contact with the surface of the second disc driven to rotate by the other roller so that the speed of rotation of the first disc is substantially proportional to the traction power output of the motor vehicle.

United States Patent Marten et a1.

[ 51 Sept. 26, 1972 [54] VEHICLE TESTING APPARATUS [73] Assignee:Suntester Limited, Kings Lynn, Norfolk, England [22] Filed: March 15,1971 [21] Appl. No.: 124,402

[52] US. Cl ..73/117, 73/134 [51] Int. Cl. ..G01l 5/13 [58] Field ofSearch ..73/117, 134, 133, 138

[56] References Cited UNITED STATES PATENTS 2,946,219 7/1960 Kemper..73/136 R 3,554,022 1/1971 Geul ..73/117 3,130,581 4/1964 Schulman..73/136 R 466,214 12/1891 Behr ..73/138 Primary Examiner-Jerry W.Myracle Attorney-Molinare, Allegretti, Newitt & Witcoff [5 7] ABSTRACTThe disclosure describes a chassis dynamometer having at least one pairof rollers for contact with at least one traction wheel of a motorvehicle, one of the rollers being braked by an eddy-current brake thestator of which is mounted for pivotal movement in accordance with thebraking torque developed against a resilient bias. A perforated disc ismounted on and for movement with the stator of the eddy-current brake,the rim of the disc being in driving contact with the surface of thesecond disc driven to rotate by the other roller so that the speed ofrotation of the first disc is substantially proportional to the tractionpower output of the motor vehicle.

11 Claims, 4 Drawing Figures VEHICLE TESTING APPARATUS RELATEDAPPLICATION Applicants hereby claim priority under 35 U.S.C. 119 basedon patent application No. 12868/70 filed Mar. 17, 1970 in Great Britainby applicants legal assignee, Suntester Limited, a British Company ofOld Meadow Road, Harwick Industrial Estate, Kings Lynn, Norfolk England.

BACKGROUND OF THE INVENTION This invention relates to chassisdynamometers, and more particularly relates to devices for measuringpower in connection with dynamometers.

Chassis dynamometers are used to measure the tractive effort or power ofmotor driven road vehicles and have at least one pair of spaced parallelrollers for driving engagement with at least one traction wheel of amotor vehicle. Braking torque is applied to at least one of the or eachpair of rollers, for example by means of an eddy-current brake. In orderto measure the power absorbed by the dynamometer, which is substantiallyequal to the power output of the vehicle being tested, it is usual bysome means or other to multiply a signal proportional to speed and asignal proportional to the braking torque of the brake.

In one previously proposed chassis dynamometer a voltage signalproportional to speed is generated by a tach-generator the resultingspeed-voltage being applied across the track of a potentiometer, theposition of the wiper of the potentiometer being determined by thebraking torque generated by the dynamometer. Such an arrangement hasdisadvantages in that suitably accurate tach-generators are oftenexpensive to buy or to manufacture. Also, if it is desired that thedynamometer should be capable of running in both a forward and a reversedirection then either the central position of the wiper on its track hasto represent zero torque, which results in half of the accuracy for agiven potentiometer, or else more complicated means have to be providedso as to insure that the direction of potentiometer wiper movement isindependent of the sense of the braking torque, i.e., the direction ofmovement is independent of the forward or reversed direction of rotationof the dynamometer rollers.

SUMMARY OF THE INVENTION In order to overcome the disadvantages of theprior art apparatus, applicants have invented improved apparatus formeasuring the power produced by a source of energy that is used to drivethe first and second rollers of a chassis dynamometer. According to apreferred feature of the invention, the apparatus comprises first andsecond rotatable members that comprise planar and circular surfaces andfirst and second axes of rotation, respectively. First means areutilized for holding the circular surface in contact with the planarsurface, and second means are utilized for applying torque in a firstdirection to the second roller. Third means rotate one of the rotatablemembers at a velocity proportional to the velocity at which the firstroller is rotated by the source. In addition, fourth means are used formoving the other rotatable member in relationship to the one rotatablemember so that the circular surface moves with respect to the planarsurface in one direction in proportion to the amount of torque appliedto the second roller in the first direction. By employing thisapparatus, the velocity of the other rotatable member is substantiallyproportional to the power absorbed by the dynamometer.

According to another feature of the invention, the apparatus comprises apair of discs, the edge of one disc being in driving engagement with aface of the other disc, one of the discs being driven at a speeddependent on the speed of rotation of the dynamometer rollers, the otherdisc being arranged for transverse relative movement dependent on thebraking torque of the dynamometer so that the speed of rotation of theother disc is substantially proportional to the power absorbed by thedynamometer.

For example, according to a preferred practice of the invention, a firstdisc of the pair may be driven to rotate by one of the said rollers, theother disc being rotatably mounted with its edge in driving engagementwith the first disc and being arranged for movement over the surface ofthe first disc and in accordance with the braking torque of thedynamometer so that the speed of rotation of the said other disc issubstantially proportional to the power absorbed by the dynamometer. Itwill be appreciated that the two discs and their respective mountingsmay be inexpensively manufactured, and that since the position of thesaid other disc which corresponds to zero torque is at the center ofrotation of the first disc the said other disc may move in either of twoopposed directions according to the sense of the torque, i.e., positiveor negative torque.

The speed of rotation of the said other disc is easily measurable inmany inexpensive ways. In the preferred form of the invention, the saidother disc has a hole or slot, or a series of holes or slots equallyspaced and arranged in a circle concentric with the axis of rotation ofthe disc, the speed of rotation of the disc being measured by meanscomprising a light source and a photosensitive device fixedly mounted onopposite sides of the disc so that it can rotate therebetween and sothat whilst rotating, flashes of light from the light source areincident through the holes on the photo-sensitive device, means beingprovided to record and/or to give a visual indication of the frequencyof a pulse output signal from the photo-sensitive device.

DESCRIPTION OF THE DRAWING These and other advantages and features ofthe present invention are hereinafter described for purposes ofillustration, but not of limitation, in connection with the accompanyingdrawing in which like numbers refer to like parts throughout, and inwhich:

FIG. 1 is a fragmentary, top plan view of a preferred form of apparatusmade in accordance with the present invention, shown in connection withthe rollers of an exemplary chassis dynamometer;

FIG. 2 is a partially schematic front elevational view of the apparatusshown in FIG. 1;

FIG. 3 is an enlarged, plan view in greater detail of one of the discsof the chassis dynamometer shown in FIGS. 1 and 2; and

FIG. 4 is a cross-sectional view of the disc shown in FIG. 3, togetherwith additional apparatus used to determine the velocity of the disc.

DESCRIPTION OF THE PREFERRED EMBODIMENT As may be seen from thedrawings, the chassis dynamometer comprises two parallel spaced androtatably mounted rollers 2 and 4.

The rollers may either be long enough to support and be driven by asource of energy, such as two traction wheels of a motor vehicle, orelse two linked pairs of rollers may be provided. The roller 4 isconnected to the rotor of a brake, in this case an eddy-current brake 6,whose stator 8 is mounted for rotational movement about the axis ofrotation of the roller 4 against a resilient bias provided by springs10. The angular movement of the stator 8 of the eddy-current brake 6 isthus proportional to the braking torque it develops.

An arm 12 is fixedly mounted on stator 8 of eddycurrent brake 6 and hasat its outer end a fork 14 in which a disc 16 is mounted by a pin 17 torotate about an axis 17a that passes through the center of pin 17.

A disc 18 is mounted for rotational movement with roller 2, and arm 12is so biased by resilient means (not shown) as to bring disc 16 intodriving engagement with a flat, planar face 20 of disc 18. Disc 16 isprovided with a rubber or synthetic rubber tire 21 that defines itscircular perimeter and a circular surface 23 (which may be for example asuitable O-ring) so as to reduce any slip between two discs 16 and 18.Further to reduce any slippage, face 20 of disc 18 has a slightly roughfinish.

The arrangement is such that when the eddy-current brake is notgenerating torque, disc 16 contacts the disc 18 in a normal positionsubstantially at its center of rotation, so that axis 18a passes throughthe point of contact 25. In addition, axes 17a and 18a are perpendicularto each other, and axis 17a is parallel to face 20. In the normalposition, axis 18a lies in the plane of circular perimeter 23. Brakestator 8 is mounted for limited rotation against resilient bias springssuch that its angular rotation is proportional to the torque generatedby brake 6. Disc 16 is rotatably mounted on arm 12 which is fixedlymounted on stator 8 of brake 6 so that, in fact, the movement of disc 16is arcuate over the surface of a faceof a disc 18. A small amount ofslippage is experienced with this arrangement, but this is found to besubstantially linear with torque, and hence is taken care of bycalibration.

As disc 16 is moved over the surface of disc 18, the speed of rotationof disc 16 depends on the product of the speed of rotation of disc 18and the distance from the center of disc 18. It will be appreciated thatin the arrangement shown, the distance of disc 16 from the center ofdisc 18 is substantially proportional to the angular deflection ofstator 8 of eddy-current brake 6. The deflection is dependent on thetorque generated by the eddy-current brake. The speed of rotation ofdisc 16 is dependent on the product of the speed of rotation of disc 20and the torque generated by the eddy-current brake. The speed ofrotation of disc 20 is dependent on the speed of rotation of the drivingwheels of the motor vehicle, and hence, the speed of rotation of disc 16is dependent on the power generated by the motor vehicle.

As may be seen from FIG. 3, disc 16 has a series of orifices 22 arrangedin a circle whose center is the center of rotation of the disc. A lightsource 24 and a photo-sensitive device 26 (in this case aphoto-sensitive transistor) are fixedly mounted on opposite sides ofdisc 16 so that when the disc rotates between them, photo-sensitivedevice 26 receives a flash of light corresponding to each orifice 22. Itwill be appreciated that the frequency of the output pulses ofphoto-sensitive device 26 is dependent on the speed of rotation of disc16 and hence on the power absorbed by the dynamometer.

In order to provide a visual indication of the power absorbed by thedynamometer, the output signal from photo-sensitive device 26 is shapedby a pulse squarer 28, and the leading edge of each output pulse fromthe pulse squarer is arranged to trigger a monostable circuit 30 so asto provide an output pulse of fixed duration and magnitude correspondingto each output pulse from the photo-sensitive device 26. Pulse outputfrom the monostable circuit is fed to a winding of a DC. ammeter 32whose deflection depends on the average value of the current passingtrough it. Since the pulse is of predetermined duration and magnitude,the average value of the current passing through the meter depends onthe frequency of the pulses, and hence, on the power absorbed by thedynamometer.

Those skilled in the art will appreciate that the preferred embodimentsdescribed herein may be altered and modified without departing from thetrue spirit and scope of the invention as defined in the appendedclaims.

What we claim is:

1. In a chassis dynamometer comprising a first roller and a secondroller adapted to be rotatably driven by a source of energy, improvedapparatus for measuring the power produced by the source comprising:

a first rotatable member comprising a planar surface and a first axis ofrotation passing through the planar surface;

a second rotatable member comprising a circular surface adapted torotate around a second axis of rotation;

first means for holding the circular surface in contact with the planarsurface;

second means for applying torque in a first direction and a seconddirection to the second roller, said second means comprising a devicethat rotates through an arcuate path having a path length proportionalto the amount of torque applied;

third means for rotating one of the rotatable members at a velocityproportional to the velocity at which the first roller is rotated by thesource; and

fourth means comprising a direct mechanical linkage between the othersaid rotatable member and said device for moving the other saidrotatable member in relationship to the one said rotatable member inopposite directions so that the circular surface moves with respect tothe planar surface along an arcuate path in proportion to the amount oftorque applied to the second roller, whereby the velocity of the othersaid rotatable member is substantially proportional to the powerabsorbed by the dynamometer.

2. Apparatus, as claimed in claim 1, wherein the first means furthercomprises resilient means for holding the first and second rotatablemembers in a normal position in which one of the axes of rotation passesthrough the point of contact of the circular and planar surfaces,whereby movement of the one rotatable member results in no movement ofthe other rotatable member.

3. Apparatus, as claimed in claim 1, wherein:

the first rotatable member comprises a first disc;

the planar surface comprises a flat face of the first disc;

the first axis of rotation is perpendicular to the flat face;

the second rotatable member comprises a second disc having a circularperimeter;

the circular surface comprises the circular perimeter;

and

the second axis of rotation is perpendicular to the plane of thecircular perimeter.

4. Apparatus, as claimed in claim 3, wherein the second axis of rotationis parallel to the flat face of the first disc.

5. Apparatus, as claimed in claim 3, wherein the circular perimeter isformed by a resilient tire.

6. Apparatus, as claimed in claim 3, wherein:

the first means holds the circular perimeter of the second disc incontact with the flat face of the first disc;

the third means rotates the first disc; and

the fourth means moves the circular perimeter of the second disc overthe flat face of the first disc.

7. Apparatus, as claimed in claim 6, wherein the second means comprisesan eddy-current brake.

8. Apparatus, as claimed in claim 7, wherein the fourth means comprises:

a stator of the eddy-current brake;

5 resilient means for limiting the movement of the stator so that theangular position of the stator is proportional to the torque generatedby the eddy-current brake; and

arm means for connecting the second disc to the stator for movementtherewith.

9. Apparatus, as claimed in claim 1, and further comprising means fordetermining the angular velocity of the other rotatable member.

10. Apparatus, as claimed in claim 9, wherein the means for determiningcomprises:

means for defining orifices in the other rotatable member that lie alonga common circle;

means for transmitting radiant energy through the means for convertingthe radiant energy transmitted through the orifices into correspondingelectrical pulses; and

means for displaying the frequency of the electrical pulses.

11. Apparatus, as claimed in claim 10, wherein the means for displayingcomprises a D, C. ammeter.

1. In a chassis dynamometer comprising a first roller and a secondroller adapted to be rotatably driven by a source of energy, improvedapparatus for measuring the power produced by the source comprising: afirst rotatable member comprising a planar surface and a first axis ofrotation passing through the planar surface; a second rotatable membercomprising a circular surface adapted to rotate around a second axis ofrotation; first means for holding the circular surface in contact withthe planar surface; second means for applying torque in a firstdirection and a second direction to the second roller, said second meanscomprising a device that rotates through an arcuate path having a pathlength proportional to the amount of torque applied; third means forrotating one of the rotatable members at a velocity proportional to thevelocity at which the first roller is rotated by the source; and fourthmeans comprising a direct mechanical linkage between the other saidrotatable member and said device for moving the other said rotatablemember in relationship to the one said rotatable member in oppositedirections so that the circular surface moves with respect to the planarsurface along an arcuate path in proportion to the amount of torqueapplied to the second roller, whereby the velocity of the other saidrotatable member is substantially proportional to the power absorbed bythe dynamometer.
 2. Apparatus, as claimed in claim 1, wherein the firstmeans further comprises resilient means for holding the first and secondrotatable members in a normal position in which one of the axes ofrotation passes through the point of contact of the circular and planarsurfaces, whereby movement of the one rotatable member results in nomovement of the other rotatable member.
 3. Apparatus, as claimed inclaim 1, wherein: the first rotatable member comprises a first disc; theplanar surface comprises a flat face of the first disc; the first axisof rotation is perpendicular to the flat face; the second rotatablemember comprises a second disc having a circular perimeter; the circularsurface comprises the circular perimeter; and the second axis ofrotation is perpendicular to the plane of the circular perimeter. 4.Apparatus, as claimed in claim 3, wherein the second axis of rotation isparallel to the flat face of the first disc.
 5. Apparatus, as claimed inclaim 3, wherein the circular perimeter is formed by a resilient tire.6. Apparatus, as claimed in claim 3, wherein: the first means holds thecircular perimeter of the second disc in contact with the flat face ofthe first disc; the third means rotates the first disc; and the fourthmeans moves the circular perimeter of the second disc over the flat faceof the first disc.
 7. Apparatus, as claimed in claim 6, wherein thesecond means comprises an eddy-current brake.
 8. Apparatus, as claimedin claim 7, wherein the fourth means comprises: a stator of theeddy-current brake; resilient means for limiting the movement of thestator so that the angular position of the stator is proportional to thetorque generated by the eddy-current brake; and arm means for connectingthe second disc to the stator for movement therewith.
 9. Apparatus, asclaimed in claim 1, and further comprising means for determining theangular velocity of the other rotatable member.
 10. Apparatus, asclaimed in claim 9, whereIn the means for determining comprises: meansfor defining orifices in the other rotatable member that lie along acommon circle; means for transmitting radiant energy through theorifices; means for converting the radiant energy transmitted throughthe orifices into corresponding electrical pulses; and means fordisplaying the frequency of the electrical pulses.
 11. Apparatus, asclaimed in claim 10, wherein the means for displaying comprises a D. C.ammeter.